Gearings with overload clutches, which in the case of overload separate the gear output from the gear input and thus interrupt drive power, are known from U.S. Pat. Nos. 4,601,218 and 4,614,134. Such overload protected gearings are provided for preference in high-power chain drive systems such as are used above all in mining, primarily in coal plough drive systems and other chain drive systems for mineral winning machines.
The known drive systems are mostly designed as double drive systems with two drive stations, i.e. the so-called main and auxiliary drive stations, at both chain reversal zones. When asynchronous motors are used at the main and auxiliary drive stations unequal load distributions occur because of electrical and mechanical imbalance, with the consequence that the electric power frequently cannot be fully utilised. The motor at the main and auxiliary drive stations are positively synchronised mechanically by means of the common chain they drive. The latter often comprises, seen over its total length, sections with different permanent chain stretches. This leads to power displacements and an irregular load distribution on the main and auxiliary drive motors. Since asynchronous motors react sensitively to variations in rotation, as is known even relatively slight variations can lead to the one of the two motors working only with partial load or even in the extreme case to one of the two motors acting as a generator. In order to achieve the optimium possible exploitation of the available electric drive power, it is known in the stated drive systems to employ a load balancing arrangement in the configuration of superposition gearing. Both the main and auxiliary drive stations may employ such gearing, usually planetary gearing, with load-dependently or rotation-rate dependently regulated motors (see U.S. Pat. No. 4,939,949 and DE-PS 3,742,342).
In the known drive systems with load balancing hydraulic motors are provided in general for operating the gearing which serves for the load balancing, but electric motors have also been proposed in the prior art for this purpose.
It is an object of the invention inter alia to develop a drive system with overload protection and load balancing facilities so that when using an electric motor for balancing it is possible to achieve an improved finely sensitive control and high operational reliability.